You can completely restrict access to your IdeaLab, either by making it a tool for internal use or making it "Invite Only" for access only by trusted partners. To do this an administrator should click on the top right drop-down and access the Admin menu. Now scroll down to the bottom of the page until you see this:
By default your IdeaLab is open to the public. If you select @Email address restricted, your ideas will not be publicly visible but instead resolve to a login page where only people who can confirm they have an email extension you have selected can login. If your company is Google.com, you would enter that here and then only people from that domain may register and access. You can also invite people by selecting invite only and uploading a CSV file with a column of email addresses. Do not include any further information other than email address. It will allow registrations only from those email addresses and otherwise be a closed system. Every person on the invite list will receive an email inviting them to signup.